The invention generally relates to a turbine, in particular a gas turbine.
In a turbine, in particular in a gas turbine of a turbo set of a power station for energy generation, a hot gas is led through the turbine. A result is that a shaft having moving blades arranged on it is driven. This shaft is connected, as a rule, to a generator for the generation of energy. The moving blades extend radially outward. Stationary guide vanes are arranged in the opposite direction, that is to say radially from the outside inward. As seen in the longitudinal direction of the turbine, the guide vanes and the moving blades engage one into the other in a tooth-like manner.
The turbine, as a rule, has a plurality of turbine stages, a guide vane ring being arranged in each stage. Thus, a plurality of the guide vanes are arranged next to one another in the circumferential direction of the turbine. The individual guide vane rings are arranged successively in the axial direction. The flow path of the hot gas through the turbine is designated hereafter as the gas space.
The guide vanes each include a vane leaf which extends radially into the gas space and is attached to a foot plate, via which the guide vane is fastened to what is known as a guide vane carrier. The individual foot plates of the guide vanes form an essentially closed surface and outwardly delimit the gas space. In order to achieve as small leakage gaps as possible between the individual foot plates, seals are provided, as a rule, between the individual foot plates.
In a conventional seal variant, the foot plate edge region is made thickened, particularly in the case of foot plates adjacent to one another in the circumferential direction, an end-face groove being worked into the thickening. For sealing, a common sealing sheet is introduced into mutually opposite grooves of adjacent foot plates.
The massive construction of the edge region in which the groove for the sealing sheet is arranged presents problems in terms of the thermal load on the foot plate. On account of the high temperatures in the turbine, the foot plates are normally cooled by way of a coolant. In this case, special cooling measures have to be taken for the massive edge region, so as not to give rise to any excessive thermal stresses between the massive edge region and the relatively thin plate region of the foot plate.
This problem is aggravated when a closed cooling circuit, for example a closed steam cooling circuit, is provided for cooling, since this does away with the possibility of guiding through the massive edge region cooling bores through which, for example, cooling air can flow. Instead, in the case of a closed cooling circuit, such bores have to be produced as blind holes, the cooling effect naturally being low in this case, since the cooling medium will scarcely flow through the blind hole to a sufficient extent.
In a further seal variant, the grooves and the sealing sheet are set back from the hot-gas side located on the gas-space side and an undercut is introduced into the massive edge region below the sealing element. Here, too, there is then again the problem of the coolant flowing through this undercut to a sufficient extent. A third seal variant, according to which cooling ducts are introduced into the body of the foot plate itself, is complicated in production terms.
In particular, here, there is the problem that, in order to form the cooling ducts during the casting of the foot plate, a core which is positioned via spacers, also has to be cast in. The core and the spacers are removed by way of suitable measures after casting, so that the cavities formed thereby can be used as cooling ducts. However, there is a connection of the cooling ducts to the outside via the cavity produced by the spacers, so that a closed cooling circuit can be implemented only with difficulty.
An object on which an embodiment of the invention may be based is, in a turbine, to design the seal between adjacent guide vanes suitably for simple cooling.
An object may be achieved, according to an embodiment of the invention, by a turbine, in particular by a gas turbine, with a gas space and with a number of guide vanes which each have a foot plate and a vane leaf extending radially from the foot plate into the gas space, a sealing element with a reception region, into which the foot plates extend, being provided in each case between the foot plates of adjacent guide vanes.
The fundamental idea of this configuration is to be seen in the reversal of the conventional sealing principle, in which a sealing sheet is introduced into corresponding grooves of the foot plates. To be precise, this necessarily requires a reinforcement of the edge of the foot plates in the groove region, thus ultimately leading to the cooling problems. In this case, in a reversal of this sealing principle, the sealing sheet is not inserted into the foot plates, but, instead, the foot plates are introduced into the sealing element. This avoids the need for a reinforcement of the edge region of the foot plate. Coolability is therefore simplified and the foot plate is cooled homogeneously in all regions, so that no thermal stresses occur.
In a preferred design, the sealing element is designed with an H-shaped cross section with two longitudinal limbs connected via a transverse limb, there being formed between the longitudinal limbs two reception regions which are separated from the transverse limb and into which the foot plates of adjacent guide vanes extend in each case. The sealing element thus partially covers the adjacent foot plates with its two longitudinal limbs, so that, in addition to the sealing property, the foot plates are held by the sealing element.
In view of assembly requirements during the production of the turbine, the sealing element is arranged preferably between guide vanes adjacent to one another in the circumferential direction of the turbine.
According to a preferred refinement, the foot plates each have a side edge bent away from the gas space, in particular radially outward, the sealing element being arranged between two side edges of adjacent guide vanes. The effective sealing height of the seal is thereby increased, without the plate thickness of the foot plate being increased. The two bent-away side edges of the foot plates in this case come to bear, in particular, on the transverse limb of the H-shaped sealing element.
In order to achieve homogeneous cooling and consequently avoid thermal stresses, the side edge has substantially the same material thickness as the remaining foot plate.
In order to prevent the sealing element from projecting into the gas space, the front side of the foot plate, the front side being directed toward the gas space, has, in the region of the sealing element, a bearing surface which is set back from the gas space and on which the sealing element lies. Preferably, at the same time, the sealing element is flush with the foot plate.
In an expedient refinement, there is, for cooling the sealing element, a flow path in the form of a leakage gap for air between the sealing element and the foot plates. There is therefore no desire to have absolute leak-tightness, in order to keep low the thermal load in the region of the sealing element and at the side edges of the foot plate. As a rule, the outside space around the gas space in a turbine is kept at a higher pressure than the gas space, so that air enters the gas space from outside via the leakage gap and the outflow of hot gas from the gas space is avoided.
In a particularly advantageous embodiment, a closed cooling system, through which a coolant is capable of flowing, is arranged in the rear region of the foot plates which faces away from the gas space, that is to say in the outside space. The coolant is in this case, in particular, steam. Alternatively, the coolant used is also a liquid, such as water, or another gas, such as air or hydrogen. Such a closed cooling system allows an effective, directional and homogeneous cooling of the foot plates and of the entire guide vanes.
Preferably, at the same time, the coolant is capable of flowing, in particular directly, over the rear side of the foot plates which faces away from the gas space, so that direct heat exchange takes place between the coolant and the foot plate.
In order to achieve an effective cooling of the foot plates, an inflow duct for the coolant is formed between an outer guide sheet and a baffle sheet, the baffle sheet being arranged between the outer guide sheet and the foot plate and having flow orifices toward the foot plate, and a return-flow duct for the cooling medium being formed between the baffle sheet and the foot plate. A closed cooling system, which has a high cooling action, is consequently implemented in a simple way. During operation, the coolant is supplied via the inflow duct and is guided at high velocity onto the foot plate via the, in particular, nozzle-like flow orifices in the baffle sheet, so that intensive heat exchange takes place between the coolant and the foot plate. The heated coolant is subsequently discharged in the return-flow duct.
Preferably, the baffle sheet is supported on the foot plate via a supporting element, so that the baffle sheet is held at a defined distance from the foot plate.
For simple fastening, preferably the baffle sheet is fastened to the bent-away side edge of the foot plate and the guide sheet is fastened, in particular, to the baffle sheet.
In order to achieve a simple mounting of the foot plates and at the same time good sealing of the foot plates both in the circumferential direction and in the axial direction between adjacent turbine stages, preferably the sealing element described is provided for sealing in the circumferential direction and a further sealing element is provided for sealing in the axial direction. Depending on the direction, therefore, and particularly for assembly reasons, differently designed sealing elements are used.
The further sealing element connects the foot plates to one another in a staple-like manner, preferably on their rear sides facing away from the gas space. The essential advantage is in this case to be seen in the staple-like configuration of the further sealing element which spans the two foot plates. The further sealing element is in this case designed to be elastic, in particular in a plurality of directions, so that, under thermal expansions, it follows the foot plates, without opening up a gap. The sealing by the further sealing element is therefore largely unaffected by thermal expansions.